PREY OF GIANT EAGLE OWLS IN THE DE HOOP NATURE RESERVE,CAPE PROVINCE,AND SOME OBSERVATIONS ON HUNTING STRATEGY

Avery, G., Robertson, A. S., Palmer, N.G. & Prins, A. J. 1985. Prey of Giant Eagle Owls in the De Hoop Nature Reserve, Cape Province, and some observations on hunting strategy. Ostrich 56: 117–122.

Prey remains of Giant Eagle Owls Bubo lacteus in the De Hoop Nature Reserve were analysed in terms of numerical composition and mass. Thirteen species of bird contributed 57,8 % of the mass, six species of mammal 41,4 %, four species of invertebrate less than 0,4 % and one species of amphibian 0;4% Black-headed Heron Ardea melanocephala was the most common bird representing 14,8 % of the mass. Accipitridae (buzzards and harriers) and Tytonidae (owls represented 10,1 % of the mass. Leporidae (hares) were the most common mammals represented 10,7% of the mass. A single bone of an adult Grysbok Raphicerus melanoris represented 20,1% of the mass and was almost certanly taken as carrion. Similarities with diet data from other areas are apparent. The Giant Eagle Owl is omnivorous, its diet being determined bayrhabitat and local abundance. Comparison with the diet of Cape Eagle Owl Bubo capensis confirms that separation of habitats, with associated differences in the accessibility and availability of prey, explains the differences in prey taken by these species.     

A synopsis of suggested approaches to address potential competitive interactions between Barred Owls (<Emphasis Type="Italic">Strix varia</Emphasis>) and Spotted Owls (<Emphasis Type="Italic">S. occidentalis</Emphasis>)

The conservation of Spotted Owl (Strix occidentalis) populations has been one of the most controversial and visible issues in United States conservation history. Coincident with declines in Spotted Owl populations over the last three decades has been the invasion of Barred Owls (Strix varia) throughout the range of the Northern Spotted Owl (S. o. caurina) and into the range of the California Spotted Owl (S. o. occidentalis). This invasion has confused the reasons behind recent Spotted Owl declines because anecdotal and correlative information strongly suggests that Barred Owls are a new factor influencing the declines. There is great uncertainty about all aspects of the invasion, and this has sparked discussion about appropriate management and research responses regarding the effects of this invasion on Spotted Owls. We present a set of possible responses to address the issue, and we discuss the relative merits of these with regard to their efficacy given the current state of knowledge. We recommend that research specifically aimed at learning more about the interspecific relationships of these two owls throughout the range of sympatry should begin immediately. Approaches that seem unlikely to be useful in the short-term either because they do not facilitate knowledge acquisition, are relatively costly, or would be technically less feasible, should not be considered viable at this time. We believe the consequences of the invasion are potentially dire for the Spotted Owl and that research and management actions, including the use of adaptive management, are required to inform the near- and long-term decision-making process for conservation of Spotted Owls.     

The Orange River avifauna: abundance,richness and comparisons

Like many other southern African rivers, the avifaunal richness and abundance of the Orange River, southern Africa's longest, remains virtually unknown. Given that the Orange River runs through hyper-arid regions in its lower reaches, its linear oasis effect and its role as a reservoir for Red Data bird species is likely but has not been quantified. Two surveys either side of the border town of Noordoewer, in the rainy and dry seasons of 1996 and 1997 deter-mined that species richness was higher in riverine habitat (71 species) than in the surrounding Nama Karoo (46 species) confirming the linear oasis effect. Surveys revealed five Namibian Red Data species. Peregrine Falcons, Falco peregrinus, and African Fish Eagles, Haliaeetus vocifer, were relatively common while the endangered Cape Eagle Owl, Bubo capensis, occurred sporadically. Among wetland Red Data bird species, Black Storks, Ciconia nigra, occurred in less disturbed areas, and White-backed Night Herons, Gorsachius leuconotus, were an unexpected species at this locality. The overall species richness of 103 birds and a density of riparian birds of 31 -3 4 birds/10 km, makes the lower Orange River avifauna similar to the Cunene River but tenfold less abundant than Namibia's other perennial rivers. Despite the low diversity, the arid habitats of the lower Orange River support greater diversity than more easterly regions when all current surveys of richness and abundance from Lesotho to the mouth on the Namib coast are combined. This east-west trend may be explained by the slower flow and warmer water of the lower Orange River but natural turbidity and regulation may explain the generally low diversity and abundance indices. Major rivers in southern Africa appear to have been over-looked as wetland habitats, and further avifaunal surveys of all of them are recommended.     

Herpersvirus strigis: host spectrum and distribution in infected owls.

Herpesvirus strigis, a new species of the genus Herpesvirus, is a pathogen for several species of owls in the order Srigiformes. Natural infection has been observed in the Eagle Owl (Bubo bubo L.), Long-eared Owl (Asio otus L.) and Snowy Owl (nyctea scandiaca L.) In addition the Little Owl (Athene noctua Scopolic) and Tengmalms Owl (Aegolius funereus L.) was experimentally infected. On the other hand the Tawny Owl (Strix aluco L.) and Barn Owl (Tyto albo Scopoli) proved resistant to a massive experimental infection. Of representatives from nine other orders of birds and mammals, only the Old World Kestrel (Falco tinnunculus L.) was found susceptible to this virus. Distribution of viral antigen in various organs of infected owls, as determined by immunofluorescence and by quantitative virus assay, was in accordance with the occurrence of macroscopic and microscopic lesions.     

Breeding density,habitat selection and reproductive rates of the Peregrine Falcon Falco peregrinus in Álava (northern Spain)

A population of 33–35 pairs of Peregrine Falcon in álava (north Spain) was studied with the aim of assessing the habitat attributes that influence breeding density, habitat selection and breeding success. A strong relationship was found between density of the species in each UTM (Universal Transverse Mercator) square of 10 × 10 km and cliff availability. Habitat selection was analysed by comparing 15 variables in 33 occupied and 25 unoccupied cliffs located at least 2 km from the nearest Peregrine pair. Significant differences were found in five variables: cliff dominance, distance to the nearest Golden Eagle Aquila chrysaetos nesting cliff, steepness and altitude (all showing larger values in occupied cliffs), and cliff orientation, with occupied cliffs facing preferably south and east. Orientation, dominance and distance to the nearest Golden Eagle pair, and the distance to the nearest Eagle Owl Bubo bubo nesting cliff, were included in a discriminant analysis which classified 82.76% of the cliffs correctly. The productivity of the studied population was 1.44 young/territorial pair (n = 45), and no consistent relationship was found between breeding success and habitat variables.     

BIOGEOGRAPHICAL AND TOPOGRAPHICAL VARIATION IN THE PREY OF THE BLACK EAGLE IN THE CAPE PROVINCE,SOUTH AFRICA

Boshoff, A.F., Palmer, N.G., Avery, G., Davies, R.A.G. & Jarvis, M.J.F. 1991. Biogeoraphical and toporaphical variation in the prey of the Black Eagle in the Cape Province, South Africa. Ostrich 62: 58–72.

Prey remains collected at or near Black Eagle Aquilu verreauxii nest sites in the Cape Province, South Africa, were analysed according to frequency of occurrence of prey scies in the samples. A total of 5748 prey individuals, collected from 73 sites, was analysed according to tree biome groups and four nest site types. The Rock Hyrax Procuvia capensis is the dominant prey species, but the eagles' diet sctrum vanestypes. The according to its availability. Indices of species richness and diversity of the prey are inverser correlated with the proportion of the prey contributed by P. capenis, which in turn is determined by topography and vegetation. Biome has a greater influence on the indices than has nest site type. The age structure of the P. capensis prey remains closely reflects the juvenile: sub- adult: adult ratios in the biomes and at the nest site tpes. hfedium-sized (aprox. 1–4,5 kg) pre is usually taken. Juvenile domestic small-stock (lambs ani goat kids) comprised onb 3,4% of the over, total.     

Environmental factors affecting patterns of distribution and co‐occurrence of two competing raptor species

Habitat selection is a complex process, that is affected by several factors, including habitat characteristics, environmental conditions, and both intra‐ and interspecific interactions. We analysed habitat preferences of two top avian predators, Peregrine Falcon Falco peregrinus, a medium‐sized diurnal raptor, and Eagle Owl Bubo bubo, a large nocturnal raptor. These two species are known to compete for preferred nest‐sites, and proximity to cliffs with Eagle Owls may reduce Peregrine breeding output through predation of young Falcons. We investigated the environmental factors affecting occurrence and coexistence of the two species and the potential role of habitat suitability in favouring co‐occurrence in 3519 km² of the central pre‐Alps of Italy, where the two species breed on cliffs and sometimes co‐occur on the same cliff. Peregrines settled on long, steep and favourably orientated cliffs in woodland landscapes close to urban areas. Eagle Owls settled on topographically similar cliffs, but in lower rainfall areas compared with cliffs occupied by Peregrines and cliffs unoccupied by either species. Sites where the two species co‐occurred were characterized by more horizontally extended cliffs compared with sites of exclusive occurrence of each species. An analysis of relative habitat suitability revealed that sites where the two species co‐occurred had the highest predicted probability of occupancy for both species, suggesting that those sites should be regarded as high‐quality sites. Breeding productivity of Eagle Owls was negatively affected by the co‐occurrence of Peregrines, whereas the effect of Eagle Owl proximity on Peregrine productivity varied according to cliff suitability for the Peregrines. Habitat selection had fitness consequences for Eagle Owls because breeding productivity increased with cliff length. Environmental conditions, particularly climatic factors, could allow the widespread coexistence of these competing raptors at the landscape scale, whereas at the local scale co‐occurrence could take place only on larger cliffs. These were preferred sites for both species, presumably because breeding at such sites offsets the costs of settling close to the competitor species.     

纵纹腹小、鵰及长耳的卵壳超微结构研究（形目：鸱科）

本文首次报道纵纹腹小、、长耳卵壳的气孔、木栅层、锥体层、乳锥体、壳膜、基底帽等结构的扫描电镜观察,并对不同种类进行分析,初步探讨了它们的分类价值和生态意义。     

Coexistence of protected avian predators: does a recovering population of White-tailed Eagle threaten to exclude other avian predators?

The processes of competition and predation determine the degree to which species can coexist; the importance of competition in particular has been emphasized at high trophic levels. Competition exclusion will occur when habitat overlap between sympatric species is high. In this study, we investigated nesting habitat overlap between internationally protected diurnal tree-nesting avian predators of central Europe, namely, White-tailed Eagle (Haliaeetus albicilla), Lesser Spotted Eagle (Aquila pomarina), Black Stork (Ciconia nigra), and Osprey (Pandion haliaetus). We found significantly different nesting habitats among the study species and suggest that this could be a consequence of the resource-based segregation, but not a consequence of asymmetrical interspecific competition. The results also show that habitat of the recovering populations of White-tailed Eagle overlapped with the habitat used by the Lesser Spotted Eagle, Black Stork, and Osprey to varying extents with a niche overlap values being below the competition exclusion threshold. Nevertheless, we suggest that competition by White-tailed Eagle at a population level may limit Osprey, though not Lesser Spotted Eagle or Black Stork.     

Superpredation patterns in four large European raptors

Predatory interactions among top predators, like superpredation or intraguild predation (IGP), can influence community structure. Diurnal raptors occupy high trophic levels in terrestrial food webs, and thus can regulate the presence of mesopredators. We studied superpredation (the killing and eating of another predator) in four large European raptors. We gathered 121 dietary studies, totalling 161,456 prey for the Goshawk Accipiter gentilis L., Golden Eagle Aquila chrysaetos L., Bonelli’s Eagle Aquila fasciata Vieillot, and Eagle Owl Bubo bubo L. Results showed that superpredation: (1) is a widespread interaction in large raptors, but it can vary according to the top predator species; (2) is not an important energetic resource for large raptors, but rather seems mostly related to diet diversification when the main prey decreases; (3) is spatially clustered reflecting habitat heterogeneity, but shows no temporal or large-scale spatial trends; and (4) it is associated with lower breeding success of the top predator species. These findings support the food stress hypothesis as the main driving force behind increases in superpredation and IGP in raptors, with the decrease in breeding performance as a side effect. Superpredation by large raptors deserves future research to understand its effects on mesopredators, because on one hand it might contribute to promote biodiversity, while on the other hand, it can sometimes represent an additional risk for small populations of endangered mesopredators.     

Geographic variation in clutch and brood size of the Eagle OwlBubo bubo in the Western Palearctic

Summary In the western Palearctic, the clutch size of the Eagle Owl (Bubo bubo) is constant with latitude and longitude whereas the brood size decreases from south to north, a reverse trend compared to other Strigiforms. This tendency seems independent of the population density of Eagle Owls and the availability of prey with high food value and may be related to climatic constraints which could determine lower viability of eggs and young at high latitudes.

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Zusammenfassung In der Westpaläarktis ist die Gelegegröße des Uhus in Gebieten unterschiedlicher geographischer Länge und Breite konstant. Im Unterschied dazu nimmt die Brutgröße von Süden nach Norden ab, umgekehrt zum Trend bei anderen Eulen. Die Tendenz der Abnahme der Brutgröße scheint unabhängig von der Siedlungsdichte und der Erreichbarkeit von Beute mit hohem Nährwert. Sie kann mit klimatischen Bedingungen zusammenhängen, die eine höhere Mortalität der Eier bzw. Nestlinge in hohen Breiten verursachen.

     

The response of the Eagle Owl (Bubo bubo) to an outbreak of the rabbit haemorrhagic disease

Summary The Eagle Owl (Bubo bubo) is a generalist predator that in Mediterranean areas feeds mainly on Rabbits (Oryctolagus cuniculus) At the end of 1997, a local outbreak of the rabbit haemorrhagic disease (RHD) decimated Rabbit populations in the area of Alicante (eastern Spain) so that Rabbit numbers in 1998 crashed to almost nil. Prior to the outbreak we had found 19 occupied Eagle Owl territories, and the owls had been feeding mainly on Rabbits. After the RHD epidemic, we found only six occupied territories and the owls were still feeding mainly on Rabbits. Diet composition was very similar between the periods, indicating that the owls did not diversify their diet in response to main prey scarcity. No significant differences in the proportion of Rabbit in the diet were found between the periods, suggesting that the impact of predation on Rabbits may be independent of the density of Rabbit populations (type I functional response). This response is not typically associated with generalist predators. In the territories that were still occupied after the outbreaks, the owls took substantial numbers of Hedgehogs (Erinaceus europaeus) and Red-legged Partridges (Alectoris rufa). Rats (Rattus spp), a common alternative prey, were not taken in the study area. Six breeding attempts were recorded before the RHD, and none after the RHD. This leads a to believe that only the combination of Hedgehog and Red-legged Partridge availability with the readier availability of sick Rabbits allowed a small population of owls to survive in the area, but did not allowed breeding. The predator-prey system formed by Eagle Owls and Rabbits in Mediterranean regions is more fragile than previously thought.

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Die Reaktion des Uhus (Bubo bubo) auf einen Ausbruch der hämorraghischen Krankheit bei Kaninchen (Oryctolagus cuniculus)

Zusammenfassung Der Uhu (Bubo bubo) ist ein wenig spezialisierter Greifvogel, der sich im Mittelmeerraum hauptsächlich von Kaninchen ernährt. Ende 1997 wurde die Kaninchenpopulation im Gebiet von Alicante (Ostspanien) durch einen Ausbruch der hämorrhagischen Krankheit (RHD) so stark dezimiert, dass der Kaninchenbestand 1998 nahezu zusammengebrochen war. Vor dem Ausbruch der Krankheit waren 19 Uhu-Reviere besetzt, und die Uhus lebten hauptsächlich von Kaninchen. Nach dem RHD-Ausbruch zählten wir nur noch sechs besetzte Reviere; die Uhus ernährten sich aber immer noch hauptsächlich von Kaninchen. Die Zusammensetzung der Nahrung war in beiden Perioden sehr ähnlich, was darauf hinweist, dass Uhus ihr Beutespektrum nicht erweitern, wenn ihr hauptsächliches Beutetier knapp wird. Dies legt nahe, dass die Anzahl geschlagener Kaninchen unabhängig von deren Populationsdichte ist (Typ I funktionelle Reaktion). Diese Reaktion ist untypisch für nicht spezialisierte Greifvögel. In den Revieren, die nach dem Ausbruch der Seuche noch bewohnt waren, fraßen die Uhus eine beträchtliche Anzahl Igel (Erinaceus europaeus) und Rebhühner (Alectoris rufa). Auf gewöhnliche alternative Beutetiere wie Ratten (Rattus spp) wurde im untersuchten Gebiet nicht zurückgegriffen. Sechs Brutversuche waren vor dem RHD-Ausbruch verzeichnet worden, danach kein einziger. Demzufolge lässt sich vermuten, dass nur der vereinte Effekt eines Igel- und Rebhuhnvorrats und darüber hinaus ein größeres Vorhandenseins kranker Kaninchen einer kleinen Anzahl der Uhus das Überleben in dem Gebiet ermöglichte, das Brüten jedoch nicht zuließ. Das im Mittelmeergebiet aus Uhu und Kaninchen bestehende Raubtier-Opfer-System ist anfälliger als bisher angenommen wurde.

     

2. RUDD'S BUSH-WARBLER (Apalis ruddi)

Gargett, V. 1982. The food requirement of a Black Eagle chick. Ostrich 53:178-181.

A hand-reared Black Eagle Aquila verreauxii chick that was fed on hyraxes, Heterohyrax brucei and Procavia capensis, ate 29 626 g from hatching to flying at 93 days. For 18 days after its first flight it ate 5 910 g, (mean 328 g per day). The eaglet's food intake increased in cold weather and decreased during a hot spell.     

Blood parasites in owls with conservation implications for the Spotted Owl (Strix occidentalis)

The three subspecies of Spotted Owl (Northern, Strix occidentalis caurina; California, S. o. occidentalis; and Mexican, S. o. lucida) are all threatened by habitat loss and range expansion of the Barred Owl (S. varia). An unaddressed threat is whether Barred Owls could be a source of novel strains of disease such as avian malaria (Plasmodium spp.) or other blood parasites potentially harmful for Spotted Owls. Although Barred Owls commonly harbor Plasmodium infections, these parasites have not been documented in the Spotted Owl. We screened 111 Spotted Owls, 44 Barred Owls, and 387 owls of nine other species for haemosporidian parasites (Leucocytozoon, Plasmodium, and Haemoproteus spp.). California Spotted Owls had the greatest number of simultaneous multi-species infections (44%). Additionally, sequencing results revealed that the Northern and California Spotted Owl subspecies together had the highest number of Leucocytozoon parasite lineages (n = 17) and unique lineages (n = 12). This high level of sequence diversity is significant because only one Leucocytozoon species (L. danilewskyi) has been accepted as valid among all owls, suggesting that L. danilewskyi is a cryptic species. Furthermore, a Plasmodium parasite was documented in a Northern Spotted Owl for the first time. West Coast Barred Owls had a lower prevalence of infection (15%) when compared to sympatric Spotted Owls (S. o. caurina 52%, S. o. occidentalis 79%) and Barred Owls from the historic range (61%). Consequently, Barred Owls on the West Coast may have a competitive advantage over the potentially immune compromised Spotted Owls.     

Nesting habitat overlap between the Common Buzzard Buteo buteo and the Lesser Spotted Eagle Clanga pomarina for conservation planning in Natura 2000 sites

Capsule: The nesting habitat of the Common Buzzard Buteo buteo and Lesser Spotted Eagle Clanga pomarina extensively overlap, indicating that they exploit similar resources.

Aim: We aimed to determine the overlap in the nest platforms, nest trees and nest stands used by these raptors, find any evidence for the avoidance of the larger Lesser Spotted Eagle by the smaller Common Buzzard, and provide conservation implications for habitat protection of the former species in habitats that overlap extensively.

Methods: Nest sites were mapped during 2012–2014 in the Bir?ai Forest Spatial Protection Area, northern Lithuania. Fifty-three nest sites occupied by Common Buzzards and 26 by Lesser Spotted Eagles were compared.

Results: The nest platforms of both raptors were similarly placed in the tree canopies. Most Lesser Spotted Eagle nests were built in spruce, while the Common Buzzard usually nested in birch. The nest stands of the eagles were on wetter soil and located closer to the forest edge than those of the buzzards, otherwise, the nest stands did not differ significantly. There was no evidence for spatial avoidance of the larger raptor by the Common Buzzard.

Conclusions: The different components of the nesting habitats extensively overlapped, and the distribution of the interspecific pairs lacked spatial avoidance. We suggest that the nest sites of both raptors were a largely shared resource, especially if located close to the forest edges. We propose, as a rule of thumb, applying protection by way of buffer zones around buzzard nest sites if they are located close to eagle nest sites and the forest edge.     

Individual acoustic monitoring of the European Eagle Owl Bubo bubo

The Eagle Owl Bubo bubo is cited in Annex I of the Birds Directive of the European Union. Europe's biggest owl is extremely sensitive to human presence and needs special conservation measures. The present paper aims to show that monitoring of individuals by bioacoustic methods can be relevant to understanding population dynamics. Our study investigates the possibility of identifying a vocal signature in the wild-recorded calls of male and female Eagle Owls, and assesses the potential use of these signatures for long-term monitoring of individuals in the field. We show that both males and females of a given population can be identified individually on the basis of their calls. Our results also show that, regardless of the sex, most of the individuals recorded in the first year of the investigation may be identical to those recorded in the same places the year after. This bioacoustic approach could thus be used in studies of site fidelity.     

Effect of great-horned owl trapping on chick survival in piping plovers

We studied the effect of great-horned owl (Bubo virginianus) removal on piping plover (Charadrius melodus) hatchling survival on Missouri River sandbars (2008–2009). Owl removal increased daily survival of piping plover chicks in 2008 (β = 2.03, 95% CI: 0.04–4.02), but this effect decreased with increasing age of the chick (β = −0.42, 95% CI: −0.81 to −0.03). Results for 2009 were similar in direction but not significant. Survival was higher in 2008 than in 2009, regardless of owl capture, indicating that even if owl capture consistently were effective at increasing survival, overall survival resulting from trapping may vary annually. Owl trapping was a successful means to raise chick survival on the Missouri River in ≥1 year and could be used at other sites experiencing depressed chick survival due to avian predators. © 2011 The Wildlife Society.     

4. GAME RESERVES IN SOUTHERN AFRICA

Steyn, P. &; Grobler, J. H. 1981. Breeding biology of the Booted Eagle in South Africa. Ostrich 52:108-118.

The Booted Eagle Hieraaetus pennatus is a breeding visitor to the Cape Province of South Africa, wintering mostly in Namibia on present knowledge. Palaearctic birds probably also reach the Cape but arrive later. Two nests in different localities in the Cape were studied. The birds breed soon after arrival. Both sexes build the nest on a cliff ledge. Incubation, which lasts 40 days, is done mostly by the female. The female spends most of her time on the nest during the first four weeks of the nestling period, but considerably less time thereafter. The male provides nearly all the prey until near the end of the nestling period, and helps to feed the young. Details of nestling growth and behaviour and of parental care are given. The nestling period was 50 and 54 days in two cases. Post-nestling dependence is about two months. Prey preferences in the two study areas were very similar: 54% birds, 33% lizards and 13% rodents. Breeding biology in South Africa is basically the same as that of Palaearctic populations, with the main differences being the habitat and cliff nest site.     

Flight strategies of migrating raptors; a comparative study of interspecific variation in flight characteristics

The comparison of flight styles and flight parameters of migrating raptors in Israel revealed the following. (1) Climbing rate in thermal circling did not differ between species, indicating that chiefly the strength of thermal updrafts determined the climbing rate and that morphological features were less relevant. (2) In interthermal gliding, air speed was positively and gliding angle negatively related to the species' average body mass. Heavier species glided faster and had smaller gliding angles. (3) In soaring and gliding flight, cross-country speed relative to the air was positively related to the species' body mass; it was obviously the result of the gliding ability increasing with body mass. (4) Eagles and buzzards used soaring and gliding flight for more than 95% of the observation time. Additional soaring in a straight line whilst gliding was extensively used by the Steppe Eagle Aquila nipalensis, Lesser Spotted Eagle Aquila pomarina and Booted Eagle Hieraætus pennatus and even more frequently by the resident species, the Griffon Vulture Gyps fulvus and Shorttoed Eagle Circaetus gallicus. Smaller species, such as the Levant Sparrowhawk Accipiter brevipes, harriers (Circus sp.) and small falcons (Falco sp.). showed the highest proportion of flapping and gliding flight (9–33%). (5) In a comparison of the flight parameters and proportions of flight styles, a cluster analysis distinguished two main groups: The first consisted of Montagu's Harrier Circus pygargus, Pallid Harrier Circus macrourus, Levant Sparrowhawk and small falcons; their flight behaviour was characterized by both the high proportion of flapping and the low gliding performance. The second group comprised the typical soaring migrants: Steppe Eagle, Lesser Spotted Eagle, Booted Eagle, Steppe Buzzard Buteo buteo vulpinus, Honey Buzzard Pernis apivorus and Egyptian Vulture Neophron percnopterus, and they had very similar flight behaviour and were closely clustered. The Black Kite Milvus migrans and Marsh Harrier Circus aeruginosus were intermediate between typical soarers and flappers. The two resident species, Griffon Vulture and Short-toed Eagle, were grouped separately from the soaring migrants.     

Wide-range dispersal in juvenile Eagle Owls (Bubo bubo) across the European Alps calls for transnational conservation programmes

Although juvenile dispersal is an important life history component, it remains one of the less understood ecological processes regulating the dynamics of animal populations. Lack of information about patterns of dispersal hampers the estimation of the actual status and demographic trajectory of populations, and can preclude the development of sound conservation strategies. The Eagle Owl Bubo bubo is an endangered bird species in the European Alps. Many breeding sites have been abandoned in the twentieth century, although some recovery has been reported lately. Moreover, the occupancy of traditional breeding sites across years in well-monitored Alpine populations varies a lot, this despite a relatively high breeding success at the population level. This raises concern about the long-term persistence of Alpine populations. Using conventional and satellite radiotracking, we investigated the spatio-temporal dispersal of 41 juvenile Eagle Owls originating from a population in the southwestern Swiss Alps. Our main goal was to determine dispersal distances, places and times of post-dispersal settlement. Juveniles left their parents between mid-August and mid-November. They covered, on average, 12.7 km per night (linear distance between two consecutive day roosts), often crossing high mountain ranges (up to 3,000 m altitude). The mean total distance covered by an individual during dispersal was 102 km (sum of night movements), with a maximum of 230 km. Settlement places were, on average, 46 km distant from the birth place. Our study establishes long-distance dispersal in juvenile Eagle Owls, even in a complex topography, suggesting the existence of a wide-scale metapopulation system across the northwestern Alps. This metapopulation dimension should be accounted for in conservation plans.